Computer systems include numerous electrical components that draw electrical current to perform their intended functions. For example, a computer's microprocessor or central processing unit (“CPU”) requires electrical current to perform many functions such as controlling the overall operations of the computer system and performing various numerical calculations. Generally, any electrical device through which electrical current flows produces heat. The amount of heat any one device generates generally is a function of the amount of current flowing through the device.
Typically, each manufacturer designs its products to operate correctly within a predetermined temperature range. If the temperature exceeds the predetermined range (i.e., the device becomes too hot or too cold), the device may not function correctly thereby potentially degrading the overall performance of the computer system. Thus, it is desirable for a computer system generally, and its components specifically, to operate within a thermally benign environment.
Some computer systems include one or more fans to blow air over the electronics to keep the electronics cool. A fan's ability to cool a computer may be a function of the volume of airflow the fan is able to move per unit of time. Both the size of the fan's blades and the speed at which the fan spins affect the magnitude of airflow. In at least some applications, it is desirable for at least some of the computer's components to be smaller rather than larger. Accordingly, including larger fans in a computer system may not be desirable. It generally may be more practical to control fan speed. Generally, faster fans provide greater cooling ability than slower fans. Fans, however, also make noise and, all else being equal, the noise level is a function of the speed of the fan; faster fans generally are noisier than slower fans.
In some computers, the fan is turned on when the computer is turned on and spun at a predetermined speed until the computer is turned off. Although generally satisfactory for cooling purposes, this approach may result in the fan continuously making a relatively large amount of noise, which may be annoying to the operator of the computer. In other computers, to reduce fan noise, a software driver may be included in the system along with hardware that together can adjust the speed of the fan(s). One or more temperature sensors may also be included to permit the system to monitor its heat load and set the fan speed accordingly. Thus, if the system is relatively cool, the fan can be made to spin at a lower speed, or even turned off to reduce the noise level. Once an increase in temperature is detected, under control of the software driver, the fan speed may be increased. A problem exists as to how to control the fan after system power is enabled, but before the software driver noted above has been loaded and able to control the fan. The subject matter described herein may address this issue.